1. Field of the Invention
The present invention relates ton computer system using a one-chip CPU for generating CPU clocks by internally performing a frequency dividing operation on an externally supplied fundamental clock.
2. Description of the Related Art
In addition, the present invention relates to a system for arbitrarily switching CPU clocks generated inside a one-chip CPU which is designed to generate the CPU clocks by internally performing frequency dividing operation on an externally supplied fundamental clock.
A microprocessor which can generate various types of operation clocks by internally performing a frequency dividing operation on an externally supplied fundamental clock EFI has been developed and is commercially available (e.g., a microprocessor known as a 386SL (tradename) available from Intel Corporation).
For example a 386.TM.SL microprocessor has a de-Turbo pin, a CPU clock register, and a de-Turbo register. In this microprocessor, either the CPU clock register or the de-Turbo register is selected in accordance with a switching signal externally supplied to the de-Turbo pin, and the frequency division ratio is changed in accordance with the value (frequency) set in the selected register, thereby changing the frequency of a clock for the microprocessor.
However, in the method of changing the clock frequency by selecting either the CPU clock register or the de-Turbo register in accordance with a signal supplied to the de-Turbo pin, after data are set in the respective registers, the clock frequency can only be changed in two steps. For this reason, it is difficult for a user to arbitrarily change the clock frequency. In addition, in the method using the de-Turbo pin, since only two types of data can be set in the de-Turbo register, the clock frequency cannot be freely changed.
For example, clocks generated by a microprocessor include clocks for a math coprocessor (e.g., a math coprocessor 387.TM.SX available from Intel Corporation). However, the user cannot switch these clock frequencies as needed.